The present invention relates to improvements in gas turbine engines and nacelles therefor and, more particularly, to a novel gas turbofan engine and nacelles therefor which exhibits lower noise levels, improved fuel consumption, greater reliability, easier maintainability, easier replaceability, and improved thrust reversal over prior art gas turbofan engines.
Considerable attention has been devoted to developing a gas turbine engine and a nacelle therefor which is quiet, clean and economical to operate. Significant improvement has been made in fuel consumption and noise levels of gas turbine engines over the past decade. Accordingly, a new family of high bypass, large diameter turbofans have recently been introduced into service. These engines have demonstrated noise levels and fuel consumption characteristics far superior to prior art gas turbine engines. The reduced noise levels of such high bypass turbofan engines is attributable to the reduced exit velocities of airflow pressurized by the fans. Though far more quiet than prior art gas turbofan engines, the recently introduced high bypass turbofan engines have higher noise levels than are desired. Thus, government regulatory agencies are applying even more stringent requirements on newly certificated commercial aircraft. The objectionable noise levels in such engines generally result from the high tip speeds of the large diameter fan blades required to efficiently pessurize the bypass duct flow. This is in contrast to the turbojet or low bypass ratio turbofan engines in which the dominant noise source results from the discharge of the hot core gas stream through its propulsive nozzle.
Another ecological problem associated with prior art gas turbine engines is that of fluid drainage. Thus, many prior art engines include fluid distribution systems in which excess fluid is not collected by any means provided by the engine and which therefore may be drained overboard onto airport runways when the engine is shut down.
While the current high bypass turbofan engines exhibit significantly lower specific fuel consumption levels than earlier engines, further improvements in specific fuel consumption are desired for both economic and fuel conservation reasons.
Another area in which improvement in the performance of prior art high bypass turbofan engines is desired is in the area of thrust reversal. One of the operational requirements of aircraft gas turbine engines is that of quick reversal from forward to reverse thrust for braking purposes after landing. Accordingly, such engines have included various schemes for reversing the forward thrust delivered by the engine. In conventional high bypass engines, this has generally been accomplished by the use of blocker doors and other apparatus for reversing the exhaust direction of the bypass stream. In addition to reversing the bypass stream exhaust direction, such engines have also has to employ mechanisms for reducing the forward thrust of the core engine. Accordingly, they have included core engine exhaust flow thrust spoilers on thrust reversers in addition to the bypass stream reversers.
Another source of problem in the design of gas turbofan engines is the means by which they are mounted to the aircraft. Prior art engines have in most instances been mounted in their installations so that the normal engine thrust loads induce some bending forces in the engine casings, giving rise to mechanical rubbing of rotating parts on stationary surfaces with subsequent reduction in performance and high repair costs.
It is therefore a primary object of the present invention to provide a economical, easily maintained gas turbofan engine with improved noise levels, fuel consumption, thrust reversal, replaceability, ecology, and mounting means.